JPS61161727A - Method and apparatus for preventing warpage of silicon wafer - Google Patents

Abstract

PURPOSE:To prevent an Si wafer to be warped, by holding Si single crystals at a temperature directly under the melting point within the atmosphere of an inactive gas under a reduced pressure and then quenching them to a normal temperature. CONSTITUTION:An apparatus consists of a section 5 for heating Si crystals and a section 6 for cooling them. The sections are isolated from each other by a gate valve 7. The heating section 5 consists of a cylindrical heater 8 made from superpure fine carbon particles and of a heating box suspended from the above at the center of the cylindrical heater and made from superpure fine carbon particles. The heating box 9 contains Si single crystals 10 within it and maintains uniform temperature distribution while they are heated at a temperature directly under the melting point. In order to improve the temperature distribution, the heating box 9 is rotatable by a pull-up device 11. The cooling section 6 is provided with a cooling gas feeding orifice 12 and a gas discharging orifice 13. Using the apparatus thus constructed, it is possible to produce Si having a high content of oxygen but a few latent oxygen cores.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for suppressing wafer warpage and a configuration of an apparatus for performing the same.

Due to the need to process a large amount of information at high speed, semiconductor devices such as ICs and LSIs, which are the main components of information processing devices, have become more densely packed, and VLSIs have come into practical use.

In other words, the size and pattern width of the semiconductor region constituting a unit element have become finer, and the minimum wiring pattern width has been reduced to 2μ.
m is in practical use.

Now, most semiconductor devices such as ICs and LSIs use silicon (St) wafers with a thickness of approximately 500 μm, and patterns are formed using thin film formation technology and photolithography. .

That is, a resist is coated on a wafer using a spin code method, etc., a fine pattern on the mask is exposed to light by contact exposure or projection exposure, and then developed and fixed to create a resist pattern, and this resist pattern is used as a mask. Fine patterns are formed on semiconductor wafers by chemical etching or dry etching.

In order to form fine patterns with high precision, it is necessary that the wafer to be processed be flat and have little warpage.

[Conventional technology]

As mentioned earlier, the thickness of Si wafers used in the manufacture of semiconductor devices such as ICs and LSIs is approximately 500 μm.
The diameter of i single crystals has increased from 4 inches to 5 inches, and from 5 inches to 6 inches.

Furthermore, as ICs become more densely packed, they are becoming more and more multi-layered.
This is done by repeatedly forming an insulating layer made of (PSG).

That is, the process of forming a wiring pattern on an insulating layer made of PSG and connecting the circuit to a wiring pattern or a semiconductor region provided on a substrate to be processed through a contact hole is repeatedly performed.

Here, in order to form the PSG layer by the CVD method, the substrate to be processed requires heat treatment at a temperature of at least 425° C. for about 30 minutes.

Therefore, the wafer undergoes several hours of heat treatment just by CvD treatment before the semiconductor device is completed, and warping occurs due to the amount of precipitated oxygen, dislocations, L: warp lines, etc. that exist inside or on the wafer surface. Easy to do.

Figure 2 shows the relationship between the amount of interstitial oxygen in a wafer and warpage.A wafer with a diameter of 4 inches and a thickness of approximately 500 μm was treated at 700°C for 50 hours under different pretreatment conditions. The results are shown below.

In other words, the solid line 1 shows the tendency for wafers that are not pretreated, and indicates that the wafer with a higher content of interstitial oxygen atoms is less likely to warp.

Moreover, the broken line 2 shows the tendency for wafers that have been annealed at 1000° C. for 16 hours in advance, and indicates that the higher the content of oxygen atoms, the greater the occurrence of warpage.

Because of this tendency, oxygen atoms in a solid solution state have the effect of suppressing the generation, proliferation, and movement of dislocations that cause warping, but if heat treatment is applied in advance to agglomerate and precipitate oxygen atoms, these effects can be suppressed. is thought to disappear.

Therefore, in order to make wafers with less warpage, the oxygen concentration must be high.
In addition, it is sufficient to prevent precipitation from occurring even if heat treatment is performed.

However, it is difficult to create such conditions, and conventionally there is no other way than to maintain the oxygen concentration of the wafer at a value near the intersection of solid line 1 and broken line 2 and use it in a state where the occurrence of warping is relatively low. There wasn't.

[Problem that the invention seeks to solve]

As mentioned above, it is known that the higher the amount of interstitial oxygen contained in a wafer, the more it suppresses warpage, but the problem is that it cannot prevent the generation of oxygen precipitation nuclei that cause dislocations. be.

[Means for solving problems]

The above problem can be solved by using a method for suppressing warpage of Si wafers, which is characterized by using a Si single crystal that is maintained at a temperature just below its melting point in a reduced pressure atmosphere of inert gas and then rapidly cooled to room temperature. I can do it.

[Effect]

In the present invention, wafer warpage is caused by a decrease in the amount of interstitial oxygen, and oxygen precipitation in the wafer only occurs when latent oxygen nuclei exist, so heating is performed at a temperature just below the melting point of Si. By doing so, the latent nucleus is diffused and dissolved,
This suppresses the reduction of oxygen atoms existing in the interstitial space.

In other words, the present invention involves melting the latent nucleus and then rapidly cooling it to freeze the state in which oxygen atoms are uniformly dissolved in solid solution to room temperature. This creates conditions in which oxygen precipitation does not easily occur even if heat treatment is applied. It is something.

〔Example〕

Solid line 3 in Fig. 1 indicates that a Si single crystal with a diameter of 4 inches and a thickness of 501 °C is heated at a temperature of 1350 °C for 1 hour in an argon (Ar): $i pressure atmosphere of 10 Torr, and then heated at a temperature of 400 °C.
This graph shows the change in oxygen concentration when a sample was rapidly cooled to 'C in 15 minutes and was treated at 700°C in a nitrogen (N2) atmosphere.The reason for choosing 700°C is that This is because the temperature is at which oxygen atoms dissolved between interstitials in the crystal are most likely to precipitate as oxygen and cause defects.

For comparison, a broken line 4 shows the results for an untreated Si single crystal that was not subjected to the present invention.

If we closely observe the solid line 3, the oxygen concentration increases slightly with the start of heat treatment, but this is because a considerable number of latent nuclei are formed in the single crystal due to the cooling of the mouth and throat that occurs during the single crystal pulling process. However, it has been shown that this is redissolved into the crystal by heating at a temperature just below the melting point, resulting in an increase in oxygen concentration.

Moreover, even if the heat treatment at 700° C. was continued thereafter, the oxygen concentration decreased only slightly.

On the other hand, the oxygen concentration of the single crystal indicated by the broken line 4 which has not been subjected to the treatment according to the present invention decreases over time, and from the above, the effectiveness of the present invention is clear.

FIG. 3 shows the configuration of a heat treatment apparatus that can easily carry out the heating method according to the present invention.

That is, this device consists of a Si crystal heating section 5 and a cooling section 6, which are separated by a gate valve 7.

Here, the heating section 5 consists of a cylindrical heater 8 made of ultra-high purity fine carbon particles and a heating casing 9 suspended from above at the center of the heater 8 and made of ultra-high purity fine carbon particles.

Here, the heating housing 9 stores the Si single crystal 10 therein, and is designed to maintain a uniform temperature distribution when heated at a temperature just below the melting point.

Note that the heater 8 and the heating casing 9 must be sufficiently air-baked in advance at a temperature of 1600° C. or higher to remove impurities in the carbon.

In order to improve the temperature distribution, the heating casing 9 is rotatably formed by a lifting device 1).

Further, the cooling section 6 is provided with a gas inlet 12 and a gas outlet 13 for cooling.

The procedure for performing high-temperature heating and rapid cooling according to the present invention using such an apparatus is as follows.

The single crystal rod grown by the single crystal pulling device is cut into appropriate dimensions to prepare the Si single crystal 10.

The Si single crystal 10 is installed in the heating casing 9 on a stand, and while gas is supplied from the gas inlet 12, it is evacuated from the exhaust port 14 using a vacuum evacuation device. The Ar pressure is maintained at about 10 Torr by adjusting the gas flow meter provided at the inlet 12, and in this state, the heating case is heated to a temperature just below the melting point, for example, 1350° C., and the heating casing is rotated.

After heating each other for a predetermined period of time, for example, one hour, the pulling device 1) is used to lift the device to the position shown by the dotted line, and with the gate valve 7 shutting off the heating section 5, N2 is supplied from the gas inlet 12. Alternatively, the heating casing 9 is rapidly cooled by blowing Ar gas.

In this way, Si with a high oxygen content but with few latent oxygen nuclei can be produced, so even when heated during the manufacturing process, less oxygen is precipitated, thus providing wafers with less warping. be able to.

〔Effect of the invention〕

As described above, by carrying out the present invention, it becomes possible to produce Ueno λ with a high oxygen content and very little warping.

FIG. 2 is a characteristic diagram showing the relationship between oxygen concentration and warpage, and FIG. 3 is a configuration diagram of the heat treatment apparatus according to the present invention.

In the figure, 5 is a heating section, 6 is a cooling section, 7 is a gate valve, 8 is a heater, 9 is a heating casing, 1
0 is a Si single crystal, 1) is a pulling device, and 12 is a gas inlet.

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Claims (2)

[Claims] (1) A method for suppressing warpage of a silicon wafer, which comprises holding a silicon single crystal at a temperature just below its melting point in a reduced pressure atmosphere of an inert gas, and then rapidly cooling it before use. (2) The device for rapidly cooling a silicon single crystal from a high temperature has a vacuum-tight structure and consists of a heating section and a cooling section separated by a gate valve, and the heating section includes a cylindrical heater and a cooling section. It is arranged in a suspended position at a central position, and includes a heating casing on which the single crystal is placed, and a cooling section that connects a winding mechanism of the heating casing and an inlet and an outlet for cooling gas. A silicon wafer warpage suppressing device comprising: